Li-ion battery having improved safety against combustion

ABSTRACT

The present invention provides a process comprising for modifying a Li-ion battery having a region of electrochemical activity and an enclosure therefor, said process comprising forming at least one chamber within said enclosure separate from said region of electrochemical activity, positioning combustion abatement agent within said chamber, whereby said combustion abatement agent is not in contact with said region of electrochemical activity, said chamber being pressure or heat sensitive, whereby when said region of electrochemical activity overheats, said chamber is breached, allowing said combustion abatement agent to contact said region of electrochemical activity to abate combustion of said region of electrochemical activity, wherein exemplary of combustion abatement agent is the composition comprising liquid fluoropolyether and exemplary of the of the chamber exhibiting pressure or heat sensitivity is to include a low melting, non-flammable polymer such as polyvinyl alcohol in the material of construction of the chamber.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/024,117, filed Jul. 14, 2014, and U.S. Provisional Application62/060,749, filed Oct. 7, 2014, which are incorporated by referenceherein in their entirety.

BACKGROUND INFORMATION

Field of the Disclosure

This invention relates to the abatement of combustion of Li-ionbatteries.

Description of the Related Art

U.S. Patent Publication 2014/0065461 discloses fluorinated materials foruse in abating the combustion of Li-ion batteries. The fluorinatedmaterials disclosed have different identities and different forms(states), i.e. solids and semi-solids. Various placements of thefluorinated material with respect to the Li-ion battery are disclosed,including placements in which multiple fluorinated materials are used.FIGS. 1, 2, 3, 4, and 5a, b, and c disclose placements outside the canof the battery, and FIG. 6 discloses placement of fluoropolymer filminside the metal foil enclosure of a prismatic type of Li-ion battery.Inside placement has the advantage of providing a combustion abatementeffect closer to the source of overheating within the Li-ion battery,which can lead to combustion.

U.S. Patent Publication 2011/0262783 (assigned to Tesla) discloses thecoating of the center pin in the region of electrochemical activity of aLi-ion battery in the jelly-roll configuration, the coating being anintumescent material, optionally having an overlayer of non-intumescentmaterial. U.S. Pat. No. 8,309,240 discloses fire-retardant materialencapsulated in a material that is electrochemically inert and thenmixing the encapsulated spheres with the electrolyte or with the anodelayer and/or the cathode layer of the Li-ion battery. Alternatively,fire retardant material is absorbed into the pores of a porous mandrel(center pin) and coated with the encapsulation material. Thus, theencapsulated fire-retardant material is installed in the region ofelectrochemical activity of the battery. The encapsulation material isdisclosed to keep the fire retardant material out of contact with theelectrolyte and electrodes until there is overheating which melts theencapsulation material, whereupon the fire-retardant material isreleased from the encapsulation.

There is a need for additional methods and Li-ion battery constructionsthat enable the fire retardant to be available inside the battery toabate combustion.

SUMMARY

The present invention provides methods and Li-ion battery constructionsfor making combustion abatement agent available from inside the batteryfor abating combustion therein.

According to one embodiment of the present invention, a process isprovided, comprising modifying a Li-ion battery having a region ofelectrochemical activity and an enclosure therefor, said processcomprising forming at least one chamber within said enclosure separatefrom said region of electrochemical activity, positioning combustionabatement agent within said chamber, whereby said combustion abatementagent is not in contact with said region of electrochemical activity,said chamber being pressure and/or heat sensitive, whereby when saidregion of electrochemical activity overheats, said chamber is breached,allowing said combustion abatement agent to contact said region ofelectrochemical activity to abate combustion of said region ofelectrochemical activity. Preferably, said chamber includes a membraneproviding the heat and/or pressure sensitivity of said chamber, wherebyit is said membrane that is breached upon the overheating of said regionof electrochemical activity.

Another embodiment of the present invention is a Li-ion batterycomprising an enclosure, structure defining a region of Li-ionelectrochemical activity positioned within said enclosure, saidstructure including oppositely charged electrodes for attracting Li-ionsfrom one said electrode to another said electrode, structure defining atleast one chamber positioned within said enclosure separate from saidregion of Li-ion electrochemical activity, said region of Li-ionelectrochemical activity being subject to overheating byshort-circuiting occurring within said region of Li-ion electrochemicalactivity, said chamber containing combustion abatement agent maintainedseparate from said region of Li-ion electrochemical activity, saidstructure defining said chamber containing said combustion abatementagent including a membrane that is breachable by said overheating tothereby release said combustion abatement agent into said region ofelectrochemical activity to abate combustion therewithin. Another aspectof this embodiment is a Li-ion battery comprising an enclosure,structure defining a region of Li-ion electrochemical activitypositioned within said enclosure, said structure including oppositelycharged electrodes for attracting Li-ions from one said electrode toanother said electrode, structure defining at least one chamberpositioned within said enclosure separate from said region of Li-ionelectrochemical activity, said region of Li-ion electrochemical activitybeing subject to overheating by short-circuiting occurring within saidregion of Li-ion electrochemical activity, said chamber containingcombustion abatement agent maintained separate from said region ofLi-ion electrochemical activity, said structure defining said chambercontaining said combustion abatement agent including a membrane that isbreachable by said overheating to thereby release said combustionabatement agent into said region of electrochemical activity to abatecombustion therewithin, with the proviso that when said membranecomprises combustion abatement agent, the presence of said combustionabatement agent in said chamber is optional. The membrane in each aspectof this embodiment is heat and/or pressure sensitive, enabling it to bebreached by overheating within said region of electrochemical activity.

By abatement of combustion or similar expression is meant that thecombustion never occurs even though the corruption of the Li-ion batteryis such that the run-away exothermic reaction is expected, or ifcombustion commences, its intensity is reduced or the fire is veryquickly extinguished. Reduced intensity means that when a plurality ofLi-ion batteries is present within the case of a battery pack, thecombustion tends to be limited to just the corrupted battery.

By pressure or heat sensitive is meant that heat and/or pressure causesrupture of the chamber. This meaning also applies to the membrane beingbreachable by overheating.

In both embodiments mentioned above, the enclosure can comprise (i)metal foil as would be the case when the Li-ion battery is the prismatictype of battery or (ii) a can as would be the case when the region ofelectrochemical activity of the Li-ion battery is in the jelly-rollconfiguration. Thus, the enclosure of the battery is that whichseparates the battery from the environment outside the battery. Theenclosure differs from a battery case, which as disclosed in U.S. PatentPublication 2014/0065461 is the container for multiple batteries.

In both embodiments, the separation of the chamber from the region ofelectrochemical activity is preferably accomplished by the chamber beingpositioned outside the region of electrochemical activity.

In both embodiments, the combustion abatement agent preferably comprisesliquid fluoropolyether. The fluoropolyether may be a mixture with solidmaterial resulting in the formation of a semi-solid. The solid materialcan be a different combustion abatement agent and/or simply a thickener.The fluoropolyether, whether in the liquid state or as a mixture withsolid material that either retains the liquid state or results in theformation of a semi-solid, can contain decomposition catalyst. Thuspreferred aspects of the present invention applicable to both theprocess and Li-ion battery embodiments are as follows:

The combustion abatement agent is a composition comprising liquidfluoropolyether. This composition additionally comprises decompositioncatalyst and/or solid material, which are preferably particulate. Thissolid material is an additional combustion abatement agent, i.e.,additional to the liquid fluoropolyether. The composition resulting fromthis liquid fluoropolyether and this solid material is a semi-solid. Thecomposition comprising the liquid fluoropolyether and decompositioncatalyst is in the liquid state under normal conditions. Liquid stateunder normal conditions and semi-solid (state) are defined hereinafter.

Preferred aspects of the Li-ion battery of the present invention, bothprocess and product embodiments, include the following:

The membrane is breachable by the overheating causing melting of saidmembrane or rupture of the membrane, such as by bursting from thepressure build up within the region of electrochemical activity.

The chamber containing the combustion abatement agent is positionedbetween said enclosure and the structure defining the region of Li-ionelectrochemical activity.

The enclosure includes a vent for pressure release upon the overheatingoccurring within the region of Li-ion battery electrochemical activity,and the chamber containing said combustion abatement agent is positionedbetween the vent and the region of Li-ion electrochemical activity. Thevent includes a closure that opens to permit pressure release, theopening of said vent accompanying the rupture of the membrane.

The vent is positioned at one end of said enclosure and an additionalchamber including a membrane that is breachable by the overheating andcontaining combustion abatement agent is positioned remote from thechamber positioned between the vent and the region of Li-ionelectrochemical activity, whereby the combustion abatement agent fromeach of the chambers is released into said region of Li-ionelectrochemical activity upon the overheating to thereby abatecombustion within the region of Li-ion electrochemical activity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematic side cross-sectional view of a Li-ion battery,illustrating one embodiment of a chamber positioned within the enclosureof a battery, separate from the region of electrochemical activity, andcontaining combustion abatement agent.

FIG. 2 is a cross-sectional view along line 2-2 of one embodiment of thebreachable portion of the chamber of FIG. 1.

FIG. 3 is a schematic side cross-sectional view of a Li-ion batteryillustrating another embodiment of a chamber positioned the enclosure ofthe Li-ion battery, separate from the region of electrochemicalactivity, and containing combustion abatement agent.

FIG. 4 is a schematic plan view of one embodiment for the constructionof a chamber containing combustion abatement agent.

FIG. 5 is a schematic cross-sectional end view of the chamber of FIG. 4.

FIG. 6 is a schematic side cross-sectional view of a li-ion battery withthe chamber of FIGS. 4 and 5 being positioned inside the enclosure ofthe battery separate from the region of electrochemical activity.

FIG. 7 is a schematic isometric view of the layers of material presentin a prismatic Li-ion battery and including chambers separate from theregion of electrochemical activity and containing combustion abatementagent.

FIG. 8 is a schematic cross-sectional view of the upper portion of theLi-ion battery of FIG. 1 modified to illustrate another embodiment ofthe present invention.

FIG. 9 is a plan view of the membrane depicted in FIG. 8.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, a Li-ion battery, within which Li-ion electrochemicalactivity occurs, comprises an enclosure 4, which in turn comprises a can6 and a battery top 8, which is the positive pole of the battery. Thecan 6 is the negative pole of the battery. The two poles are insulatedfrom one another by a u-shaped insulator ring 10 positioned between thepositive and negative poles where proximate to one another. Positionedwithin the u-shape of the insulator ring 10 is a disc 12 having anaperture 14 therewithin and a rupture disc 16 forming a closure ofaperture 14. The elements 8, 12, and 16 are shown spaced from oneanother for clarity. In practice these elements are pressed together,either directly or through the presence of shims (not shown) by thecrimp 18 encircling the can 6 as shown.

The sides of the can 6 and sheet insulators 22 and 24 define thestructure that forms the enclosure of the region of electrochemicalactivity. The region of electrochemical activity 20 comprises anelectrode assembly, including oppositely charged electrodes forattracting Li ions to pass from one of these electrodes to another ofthese electrodes through a separator containing electrolyte. Thiselectrode assemblage is rolled up like a jelly-roll about a center pin26, which is hollow as shown. This is the structure defining the regionof electrochemical activity 20, except the lengths of the center pin 26extending above and below insulators 22 and 24, respectively, areoutside the region of electrochemical activity 20. The electrodes of thejelly-roll assemblage are appropriately connected to the can and batterytop to provide for their positive and negative polarity. Typically, aninsulating sheet (not shown) is positioned between the can 6 and regionof electrochemical activity 20. For simplicity, the details of theregion of electrochemical activity are not shown in FIG. 1 (and FIGS. 3and 6). This electrode assembly has the appearance and constituency ofthe layers 58-66 of the battery 55 of FIG. 7, but rolled up upon itself(jelly roll).

The combination of the structure comprising the enclosure 4 (can 6 andbattery top 8), the insulator ring 10, the rupture disc 16 and the topinsulator 22 of battery 2 is the structure defining a chamber 28 that isseparate from the region of electrochemical activity 20 which is subjectto overheating by short-circuiting. Combustion abatement agent ispositioned and contained within this chamber and is represented in FIG.1 and the remaining Figures by stippling. The chamber 28 is positionedbetween the enclosure of the battery, in particular, the can 6 andbattery top 8, and the region of electrochemical activity 20 andoverlies and is coextensive with a substantial portion of the region ofelectrochemical activity 20. Preferably, the hollow interior of thecenter pin 26 does not contain combustion abatement agent. The hollowcenter pin 26 may be plugged to prevent entry of the combustionabatement agent into the interior of the center pin if desired. Thisentry can be prevented by controlling the height of the combustionabatement agent in the chamber 28 to be less than the height of thecenter pine 26 extending into the chamber 28. The top insulator 22serves as a pressure and/or heat sensitive membrane of the chamber 28.The rupture disc 16 is preferably primarily pressure sensitive. The topinsulator 22 forming the underside of the chamber 28 keeps thecombustion abatement agent out of contact with and therefore separatefrom the region of electrochemical activity until the region ofelectrochemical activity overheats, causing the breaching of topinsulator 22, thereby allowing the combustion abatement agent to contactthe region of electrochemical activity to abate combustion.

Because the center pin 26 is surrounded by the electrode assembly, it iswithin the region of electrochemical activity, whereby the center pin,both its outside surface and its hollow interior, are not separate fromthe region of electrochemical activity 20. The chambers within whichcombustion abatement agent is positioned according to the presentinvention are substantially separate from the center pin. Thus, thesmall extension of the center pin 26 into chamber 28 in FIG. 1 is notessential to the combustion abatement effect achieved by release of thecombustion abatement agent from chamber 28 onto the electrode assemblagewithin the region of electrochemical activity 20. Moreover this smallextension of the center pin 26 into chamber 28 is outside the region ofelectrochemical activity 20.

In operation, when the Li-ion battery is corrupted within the region ofelectrochemical activity, this region overheats and this overheating isaccompanied by an increase in pressure. This overheating and increase inpressure, individually or in combination, causes breaching of the topinsulator 22. This breaching releases the combustion abatement agentfrom chamber 28 into the region of electrochemical activity 20, enablingthe agent to abate this combustion. The pressure developed within theregion of electrochemical activity may be sufficient to cause rupture ofrupture disc 16, whereby the aperture 14 covered by the rupture discserves as a vent for pressure release from the battery. The volatile gasaccompanying this rise in pressure cause by overheating occurring withinthe region of electrochemical activity is allowed to escape from thebattery by an aperture (not shown) in the battery top 8.

The positioning of the chamber 28 between the region of electrochemicalactivity 20 and the vent (aperture 14) has the effect of couplingpressure release from inside the battery with release of combustionabatement agent into the region of electrochemical activity to abatecombustion.

To aid in the breaching of top insulator 22, the insulator 22 is scoredwith an array of lines 30 extending away from the aperture 32 throughwhich the center pin 26 fits as depicted in FIG. 2. This scoring weakensthe insulator 22, thereby promoting its breach in response to theheat/pressure occurring from corruption of the battery within the regionof electrochemical activity.

Depending upon the magnitude of the overheating and pressure build-upwithin the region of electrochemical activity, the rupture disc 16 canalso burst to permit escape of volatiles from the region ofelectrochemical activity through chamber 28. The presence of the rupturedisc 16 is optional, since the top insulator 22 acts to release pressuredeveloped within the region of electrochemical activity. If the rupturedisc were not present, the aperture 14 would serve to relieve batteryinternal pressure. The presence of the rupture disc 16, however, servesto protect the chamber 28 from entry of impurities during storage,handling, and use. The combustion abatement agent can be loaded into thechamber 28 prior to installation of the rupture disc 16, if any.

The rupture disc 16 can also be scored to assist in its rupture.Alternatively, one or both the top insulator 22 and rupture disc 16 canbe of low melting material, whereby the overheating within the region ofelectrochemical activity is sufficient for the top insulator or rupturedisc, as the case may be, to melt. The melting of the top insulator 22will release the combustion abatement agent onto the region ofelectrochemical activity, and the melting of the rupture disc 16 willallow volatiles to escape from the battery. This escape will of coursebe moderated and rendered unnecessary by the combustion abatement agentfrom the chamber 28 abating combustion within the region ofelectrochemical activity 20. The melting of the top insulator 22 alsofacilitates its rupture under the pressure increase within the region ofelectrochemical activity upon corruption of the battery.

An example of a material of construction from which the sheet of topinsulator 22 and the rupture disc 16 can be made is a hydrocarbonpolymer such as polyvinyl alcohol, which is a low melting polymer,melting temperature of 180° C. to 190° C., having the property of beingelectrically insulating and subject to charring upon heating above themelting temperature. Another example of a material from which the sheetof top insulator and the rupture disc can be made is polyvinylidenefluoride, a low melting polymer, melting temperature as low as 170° C.,which is flame resistant and does not support combustion. Lower meltingelectrically insulating polymers can be used are the hydrocarbonpolymers such as polyethylene or polypropylene, which melt attemperatures above 100° C. Higher melting hydrocarbon polymer, such aspolyamide, can be used, wherein pressure sensitivity achieved byscoring, will be the primary mechanism for breaching of the insulator 22or rupture disc 16. Preferably the hydrocarbon polymers just mentionedare flame retardant, i.e. contain one or more flame retardants effectiveto impart non-flammability to the polymer. Examples of flame retardantsinclude those containing bromine, such as decabromodiphenyl ether, thosecontaining phosphorus such as dimethyl methylphosphonate, and mineralsuch as aluminum trihydrate. Preferably, the material of construction ofthe top insulator 22 and rupture disc 16 has a melting temperature of atleast 100° C. Preferably, the melting temperature is no greater than350° C., more preferably no greater than 200° C. Preferably, thematerial of construction at least of the top insulator 22 is inert withrespect to the Li-ion electrochemical activity occurring within theregion of electrochemical activity in its normal operation and iselectrically insulating. Alternatively, the rupture disc can be metalthat is either scored or has pressure sensitive attachment bridging theaperture 14.

The elements numbered the same as FIG. 1 in the remaining Figures arethe same as in FIG. 1. In FIG. 3 the battery of FIG. 1 is modified tobattery 40 having a second chamber 42 within the enclosure 4 at thebottom of the battery and defined by the bottom of the can 6 and thebottom insulator 24 being spaced, such as by shimming (not shown) fromthe bottom of the can. The second chamber 42 is in effect positionedwithin the enclosure 4 for the battery, e.g. at one end, that is remotefrom the aperture 14 defining the battery vent and the chamber 28, e.g.at the opposite end of the battery. The combustion abatement agent canbe loaded into chamber 42 prior to installation of the region ofelectrochemical activity 20 into the can 6. The chamber 42 can bepresent in the battery 2 in combination with chamber 28 or in placethereof, i.e. no chamber 28. When combustion abatement agent ispositioned in both chambers 28 and 42, the effect of volatiles headingto the top chamber 28 and aperture 14 draws combustion abatement agentfrom the bottom chamber 42 into the region of electrochemical activity20, resulting in release of combustion abatement agent from bothchambers into the region of electrochemical activity. This abatescombustion within this region. The bottom insulator 24 can be scoredsimilar to that of the top insulator 22 as shown in FIG. 2, and can bethe same or different from the material of construction as the topinsulator 22 to serve as the heat and/or pressure sensitive membrane ofchamber 42. The chamber 42 is coextensive with a substantial portion ofthe region of electrochemical activity 20. As depicted in FIGS. 1 and 3,the chambers 28 and 42 are coextensive with the top and bottom, i.e.opposite ends, of the region of electrochemical activity 20.

FIG. 4 is directed to a different embodiment for providing the chamberseparate from the region of electrochemical activity and being withinthe enclosure 4 of the battery. In FIG. 4, multilayer sheet 48 is showncomprising a bottom film 50 and a top film 52 spaced from the bottomfilm to form a chamber 54 filled with combustion abatement agent as bestshown in FIG. 5. To form this chamber, the combustion abatement agentcan be applied as a uniform layer to bottom film 50, keeping the sideborders of the film 50 clean (uncovered). The top film 52 can then beplaced on top of the layer of agent, followed by heat sealing overlyingside borders of each film together. The heat sealed borders will bethinner than the separated film layers forming the chamber 54. Ifdesired, strips (not shown) of the same polymer as the films 50 and 52can be heat sealed (bonded) to the border lengths to bring the thicknessof the border area to be the same as the chamber area. Instead of heatsealing, the overlapping borders of films 50 and 52 and strips of filmcan be adhered together by an adhesive. The material of construction offilms 50 and 52 can be the same as form top insulator 22. Thus, thefilms 50 and 52 are membranes that are breachable by overheating withinthe region of electrochemical activity to release the combustionabatement agent into the region of electrochemical activity 20.

In FIG. 6, the multilayer sheet 48 is positioned inside the Li-ionbattery between the can 6 and the outer surface of the jelly rollassemblage forming the region of electrochemical activity 20. As withthe chambers 28 and 42, the chamber 54 is positioned within the batteryenclosure 4, but outside the region of electrochemical activity 20 andis coextensive with a substantial portion of the region ofelectrochemical activity 20. This provides a cylindrical sheath ofcombustion abatement agent surrounding the side of the region ofelectrochemical activity 20. As shown in FIG. 6, this embodiment can becombined with the embodiments of FIGS. 1 and 3, which position thecombustion abatement agent at top and bottom of the region ofelectrochemical activity 20, thereby surrounding the region ofelectrochemical activity with chambers containing combustion abatementagent. Alternatively, the chamber 54 can be combined with only one of,or none of, the chambers 28 and 42. The film 50 facing the region ofelectrochemical activity is the heat and/or pressure sensitive membranefor chamber 54 and can be scored (not shown) to assist in its breachingin response to overheating within the region of electrochemical activity20.

The structure defining the chambers, such as chambers 28, 42, and 54,defines an empty space or void that contains combustion abatement agentthat is different from the defining structure. The defining structureitself can include combustion abatement agent, which is neverthelessdifferent from the combustion abatement agent contained in the chamber.

FIG. 7 shows another embodiment of the present invention wherein thebattery is the prismatic battery 55 made up of a stack of layers ofmaterials, as follows:

-   -   metal foil 56 forming the top and bottom layers of the battery        55,    -   multilayer sheet 48 each forming a chamber 54 filled with        combustion abatement agent adjacent each metal foil layer,    -   anode current collector layer 58 adjacent to one of the layers        48,    -   ionically active layer 60 adjacent to anode current collector        layer 58,    -   cathode current collector layer 62 adjacent to the other        multilayer sheet 48,    -   ionically active layer 64 adjacent to the cathode current        collector layer 62, and    -   porous separator layer 66 positioned between the layers 60 and        64.

For simplicity, the metal foil layers 56 are not shown enveloping thesides of the other layers to form the enclosure (pouch) of the battery55, and tabs of the anode and cathode current collectors are not shownextending through the pouch for electrical connectivity.

The metal foil layers 56 are preferably of aluminum and are preferablycoated (not shown) on both surfaces (top and bottom) with polymer forelectrical insulation purposes. Further mention of the metal foil layerincludes the preference for these polymer coatings being present on themetal foil of the metal foil layer. The polymer coating on the surfaceof the metal foil layer 56 facing the outside of the of the battery ispreferably polyamide and the polymer coating of the surface of the metalfoil layer facing the inside of the battery is preferably polypropylene.The anode current collector layer 58 is preferably copper, and thecathode current collector 62 is preferably aluminum. The multilayer film48 can be in contact with their respective current collector layers 58and 62. The multilayer film 48 can also be in contact with theirrespective metal foil layers 56. The multilayer film 48 can be separatefrom, i.e. not bonded to, the adjacent metal foil layer and/or theadjacent current collector layer. As an aid to understanding FIG. 7,i.e. to distinguish layer formed from multilayer film 48 from the otherlayers depicted in FIG. 7, the multilayer film 48 is depicted in FIG. 7as containing combustion abatement agent in its respective chamber 54.The ionically active layers 60 and 64 are preferably coatings on theirrespective current collector layers 58 and 62. An example of the layer60 is lithiated graphite and binder, and an example of the layer 64 islithiated metal oxide and binder. The combination of layers 58 with 60and 62 with 64 form the electrodes of the battery. The porous separatorlayer 66 is a porous material containing electrolyte, the porespermitting the passage of lithium ions during discharge. The porousmaterial separator may be polymeric, wherein the polymer is by itselfhydrophilic or has a hydrophilic coating on the surfaces of theseparator, including its pores. Overheating within the region ofelectrochemical activity 20, results in melting and/or rupturing (bybursting) of the films making up multilayer film 48, thereby releasingcombustion abatement agent to abate combustion of the battery. Thelayers 58-66 represent the region of electrochemical activity 20 withinthe enclosure formed by layers 56 of the battery 55. The layers 48containing the combustion abatement agent are positioned within thisenclosure but outside the region of electrochemical activity 20, theboundaries of which as defined by layers 58 and 62. Thus, during normaloperation of the battery, the combustion abatement agent is keptseparate from the region of electrochemical activity.

Identification of the insulator 22 and insulator 25 (FIGS. 1 and 3) astop and bottom insulators, respectively, and to the multilayer sheet 48being present adjacent to the top layer and bottom layers of theprismatic battery of FIG. 7 is with reference to the orientation of thebatteries depicted in these drawings. For both this orientation anddifferent battery orientations, the top and bottom locations can beidentified as being one end of the battery and the opposite end of thebattery, respectively. Once the ends of the battery are identified, thenthe remaining location for positioning a chamber containing combustionabatement agent can be identified as the side(s) of the battery.

In addition to chambers such as chambers 28, 42, and 54 described above,the Li-ion battery can be equipped with other safety features such acircuit interrupter.

The coextensivity of the chambers 28, 42, and 54 with substantialportions of the region of electrochemical activity 20 includecoextensivity with substantial portions of the opposing surfaces of theregion of electrochemical activity. Preferably, the heat and/or pressuresensitive membranes included in the structure defining each chamber isin contact with the outer surface of the region of electrochemicalactivity 20 and is preferably electrochemically inert, i.e. does notadversely affect the normal electrochemical activity of the region ofelectrochemical activity in its normal operation. Preferably, the Li-ionbattery to which the embodiments of the present invention are applicableis a secondary battery, i.e. is rechargeable. These embodiments are alsoapplicable to primary Li-ion batteries.

The Li-ion battery 70 of FIG. 8 incorporates these principles. Thebattery 70 comprises a can 72, within which is contained a region ofelectrochemical activity 20 surrounding center pin 26. Top insulator 74is positioned on top of the region of electrochemical activity 20 and isclamped thereto by crimp 73 in the side of can 72. The top insulator 74has a flat periphery 76 and a domed central portion 78. The topinsulator is annular in shape as best depicted in FIG. 9, and domedcentral portion 78 has score lines 80 to facilitate its rupture uponexposure to heat and pressure from region of electrochemical activity 20when corrupted.

The battery also has a battery top 88 serving as the positive pole ofthe battery. Top 88 is held in place by clamping between crimp 73 andflange 82. The top 88 contains a vent 84 in the form of a cylindricalopening in the top bounded by a short stack. A pressure release closure86 is provided for the opening in the top of the short stack and issecured to the short stack of the vent 84 or top 88 by conventionalmeans (not shown).

The top insulator 74 or at least the domed central portion 78 ispreferably made of combustible abatement agent, such as thermallydestabilizable fluoropolymer, examples of which are describedhereinafter and which are capable of being fabricated into the topinsulator structure. This serves as the membrane that is breachable byoverheating within the region of electrochemical activity 20. Thisoverheating is accompanied by the development of pressure within theregion of electrochemical activity, arising from the corruption withinthis region, characteristic of the battery embodiments of FIGS. 1, 3, 6,and 7. This results in the breaching of top insulator, by rupture alongthe score lines 80. In the embodiment of FIG. 8, rupture along scorelines does more than release the pressure build-up within the region ofelectrochemical activity 20. Since the combustion abatement agent suchas thermally destabilizable fluoropolymer from which the top insulator74 or at least the domed central portion 78 is made reacts to depletevolatile combustibles under the conditions of corruption to contributeto or accomplish combustion abatement. The resultant volatiles exitingthe battery via top 88 through vent 84, upon pressure-assisted removalof closure 86, are noncombustible. Further contributing to combustionabatement is the melting of the combustion abatement agent such as thethermally destabilizable fluoropolymer, resulting in molten agententering the region of electrochemical activity 20 to provide combustionabatement.

In one embodiment, the thickness of the top insulator 74 or at least thedomed central portion 78 provides enough combustion abatement agent suchas thermally destabilizable fluoropolymer to accomplish the combustionabatement. The score lines 80 are deep enough into this thickness, toenable breaching in response to the overheating with the region ofelectrochemical activity 20.

In another embodiment, the empty chamber 90 within the battery 70, whichis formed (defined) by top insulator 74, the battery top 88, and thecrimp 73 in the battery can 72, contains combustion abatement agent (notshown in FIG. 8). The combustion abatement agent can be added to thechamber 90 prior to application of the battery top 88 to the battery.The amount of combustion abatement agent added to the chamber 90 canrange from providing a layer on top of the top insulator 74 to fillingup the chamber 90 to the extent possible in the process of assemblingthe top 88 with the battery can 72. The combustion abatement agentpresent in chamber 90, but not shown in FIG. 8, at least supplements thecombustion abatement effect of the top insulator 74.

The chamber 90 in FIG. 8 is similar to chamber 28 in the batteries ofFIGS. 1 and 6, one difference being the presence of rupture disc 16 inchamber 28 in the batteries of FIGS. 1, 3 and 6, but not in the batteryof FIG. 8. As is apparent from the construction defining the chamber 90,the rupture disc 16 can be eliminated from the structure definingchamber 28, resulting in volatiles passing directly from chamber 28 toand through the vent (not shown) in the battery top 8 of FIGS. 1, 3, and6. Alternatively, the rupture disc 16 can be incorporated into theconstruction of the battery 70 in FIG. 8, thereby becoming the top ofthe chamber 90.

The thermally destabilizable fluoropolymer as a combustion abatementagent itself is another material of construction from which the bottominsulator 24 (FIGS. 1, 3, and 6) and the films 50 and 52 (FIG. 5) can bemade.

The option of chamber 90 in FIG. 8 being empty, i.e. free of combustionabatement agent, can be applied to the chambers 28 and 42 at the top andbottom, respectively, of the battery (FIGS. 1, 3, and 6) when theirrespective insulators comprise combustion abatement agent such asthermally destabilizable fluoropolymer to provide the combustionabatement effect. The insulators 22 and 24 constitute the overheatingbreachable membranes of their respective chambers. Thus, when any ofthese membranes comprise combustion abatement agent such as thermallydestabilizable fluoropolymer, the presence of combustion abatement agentin the chamber is optional. It is preferred, however, that the chambersat the top and/or bottom of the battery contain combustion abatementagent. Combustion abatement agent is present in chamber 54 of theembodiment of FIGS. 4 and 5

The design of the top insulator 74 having a domed central portion 78,which as shown in FIG. 8 covers the end of the center pin 26, can beused in other battery embodiments of the present invention, such assubstitution for top insulator 22 in the batteries of FIGS. 1, 3, and 6.The use of this design is not limited to the material of constructionbeing thermally destabilizable fluoropolymer. The material ofconstruction can be any of the materials described above as the materialof construction for top insulator 22. The combustion abatement agent isof course itself non-combustible.

The combustion abatement agent can be a single material or a mixture ofmaterials that provide the combustion abatement effect on the corruptedLi-ion battery. Such material(s) can exhibit one or more modes of actionin providing the combustion abatement effect, such modes of actionincluding (i) heat absorption, (ii) dilution of combustibles, (iii)becoming intumescent, (iv) forming char, and/or (v) depletion ofcombustibles. The combustion abatement agent is capable of responding tothe corruption of the Li-ion battery with multiple modes of action.

Concerning mode of action (i), agents that absorb heat contribute to theabatement of combustion by removing heat from the potential or actualcombustion site within the Li-ion battery. Heat drives the combustionreaction. Removal of this heat abates the combustion. Concerning (ii),dilution of combustibles retards the combustion reactions by barring thecombination of combustible species such as oxygen and hydrogen thatwould otherwise support the combustion process. Concerning (iii) and(iv), these are related in that the charring effect may be the result ofintumescence exhibited by the combustion abatement agent whensufficiently heated. Intumescence, however, can be obtained withoutcharring. In either case, preventing its spread or choking off the entryof outside oxygen (air) into the combustion zone. Thus, the char andintumescent structure forms a barrier to combustion. Concerning (v), thenon-combustible volatiles emitted by the combustion abatement agentcombine with combustible active species such as oxygen and hydrogen torender them non-combustible.

In one embodiment, a preferred combustion abatement agent isfluoropolyether, which is a liquid under normal conditions (15° C. to25° C.) and preferably under normal operation of the Li-ion battery(temperatures up to 80° C.) at one atmosphere of pressure. This liquidstate means that the fluoropolyether does not emit volatiles during thetemperatures up to 40° C., sometimes up to 50° C., or up to 60° C. andeven up to 80° C. (one atmosphere pressure). The boiling temperature ofthe fluoropolyether is preferably at least 80° C., more preferably atleast 100° C. and more often at least 150° C. (one atmosphere pressure).

The liquid state arises from the fluoropolyether having a low molecularweight relative to the molecular weight of solid fluoropolymer. Solidfluoropolymer will generally have a molecular weight of at least 50,000,while fluoropolyether will generally have a molecular weight in therange of 800 to 15,000 or 1,200 to 15,000. The preferred fluoropolyether(FPE) is the perfluoropolyether (PFPE). Any mention of fluoropolyethers(FPE) herein includes perfluoropolyethers (PFPE). The fluoropolyether isa mixture of different molecular weights. In the PFPE, all monovalentsubstituents on chain carbon atoms are fluorine. The FPE ischaracterized by having a chain structure in which oxygen atoms in thebackbone of the molecule are separated by saturated fluorocarbon groupshaving 1-3 carbon atoms, preferably perfluorocarbon groups as in thecase of the PFPE. More than one type of fluorocarbon group may bepresent in the FPE molecule. Representative structures are(—CFCF₃—CF₂—O—)_(n)  (I)(—CF₂—CF₂—CF₂—O—)_(n)  (II)(—CF₂—CF₂—O—)_(n)—(—CF₂—O—)_(m)  (III)(—CF₂—CFCF₃—O—)_(n)—(—CF₂—O—)_(m)  (IV)

These structures are discussed by Kasai in J. Appl. Polymer Sci. 57, 797(1995) and they are commercially available as certain KRYTOX® andFOMBLIN® lubricating oils. Preferably, the FPE has a carboxyl group atone end or at both ends of the chain structure of the FPE. Formonocarboxyl FPE, the other end of the molecule is usuallyperfluorinated as in the case of PFPE but may contain a hydrogen atom.FPE, whether having a carboxyl group at one or both ends, have at least2 ether oxygens, more preferably at least 4 ether oxygens, and even morepreferably at least 6 ether oxygens, i.e. n in the formulae above is atleast 2, 4, or 6 and m in the formulae above is at least 1, 2 or 3.Preferably, at least one of the fluorocarbon groups separating etheroxygens, and more preferably at least two of such fluorocarbon groups,has 2 or 3 carbon atoms. Even more preferably, at least 50% of thefluorocarbon groups separating ether oxygens have 2 or 3 carbon atoms.Also, preferably, the FPE has a total of at least 9 carbon atoms. Themaximum value of n and m in the formulae above is preferably that whichdoes not exceed the molecular weight at which the composition is liquidunder normal conditions and preferably under normal operation of theLi-ion battery. While more than one FPE including can be used in thesemi-solid composition of the present invention, preferably only onesuch FPE. The FPE is a mixture of different molecular weights, acomposition, wherein the n or m value given is the average number of nand m groups present in the FPE.

The FPE and especially the PFPE have high thermal stability. Whenthermally unstable end groups, such as carboxyl, are present in the FPE,the heat provided by the corrupted Li-ion battery, causes thedecarboxylation of the FPE (and PFPE). This decarboxylation contributesnon-flammable volatiles to abate combustion. The overheating of thecorrupted battery can also cause the fluoropolyether to decompose,thereby emitting non-combustible volatiles that combine with combustibleactive species such as oxygen and hydrogen to render themnon-combustible (mode of action (v)). The liquid fluoropolyether canexhibit the additional combustion abatement effect of preventingcombustion from occurring when present at the combustion site beforecombustion begins.

The thermal stability of the liquid fluoropolyether can be reduced byincorporating decomposition catalyst into the fluoropolyether. Thedecomposition catalyst operates thermally, i.e. in response to heatingof the fluoropolyether as occurs upon corruption of the Li-ion battery.The decomposition catalyst lowers the temperature of decomposition ofthe fluoropolyether, resulting in earlier emission of non-combustiblevolatiles that abate combustion of the Li-ion battery. The preferreddecomposition catalyst is Lewis acid, such as AlCl₃, BF₃, FeCl₃ andTiCl₄. Preferably these are particulate solids under normal operatingconditions of the Li-ion battery. Only a small amount of catalyst isnecessary to be effective in causing decomposition of thefluoropolyether upon its heating by the corrupted Li-ion battery. Forexample, the amount of catalyst, such as Lewis acid, present in thefluoropolyether is 0.1 to 2 wt % based on the weight of thefluoropolyether.

In another embodiment, the combustion abatement agent can be a solid,typically in the particulate form, under the operating conditions of theLi-ion battery, and typically an inorganic compound.

Examples of combustion abatement agents include those compounds that,upon thermally-induced decomposition, emit water, nitrogen, nitrogendioxide, carbon dioxide, or sulfur dioxide, which contribute to modes ofaction (i) and (ii). Examples of these compounds include hydrate,carbonate, bicarbonate, sulfate, bisulfite and bisulfate. Specificcompounds include Al(OH)₃, sometimes represented as Al₂O₃.3H₂O, Mg(OH)₂,borax (Na₂B₂O₇.10H₂O), Zn borate, and sepiolite, a mineral that ishydrated magnesium silicate. The release of water from hydrates isconsidered decomposition. Al(OH)₃, for example releases water uponheating to about 180° C.

Additional compounds that are combustion abatement agents include thealkali and alkaline earth metal carbonates, bicarbonates, sulfates,bisulfites, and bisulfates, such as sodium, potassium, calcium andmagnesium carbonate, bicarbonate, sulfate, bisulfite and bisulfate.Examples of nitrogen or nitrogen dioxide emitting compound includemelamine and melamine cyanurate.

The combustion abatement agent can become a char and/or exhibitintumescence upon heating (modes (iii) and (iv)), such agents includingsodium silicate, vermiculite and graphite. Except for graphite, thesecompounds are preferably inorganic. The combustion abatement agent canbe a heat absorbing solid such as carbon. Carbon can be consideredsimply as a single element compound as distinguished from the inorganiccompounds mentioned above.

The combustion abatement agent can be phosphorus containing, andpreferably inorganic, such as ammonium polyphosphate ([NH₄PO₄]_(x)),alkali metal or alkaline earth metal orthophosphate or pyrophosphate,which contribute combustion abatement through mode of action (v). Thecombustion abatement agent can be an organic compound such as one thatis bromine containing, examples of which are organic bromine-containingcompounds such as carbon tetrabromide, tetrabromo-bisphenol A andtris(tribromoneopentyl) phosphate.

From the foregoing, it is apparent the combustion abatement agents thatare inorganic compounds, carbon, or organic compounds and preferablynon-polymeric. These are combustion abatement agents other thanfluoropolymers that are thermally destabilized as described below.

In another embodiment, the combustion abatement agent is a solidfluoropolymer which is non-flammable and decomposes under overheating bythe corrupted Li-ion battery to emit volatile species that abate thecombustion. Preferably, the solid fluoropolymer is thermallydestabilizable so as to provide this decomposition in response tocorruption of the Li-ion battery. This fluoropolymer can have a widevariety of identities to be described hereinafter, all of which are inthe solid state. In general, the fluoropolymer has a carbon atombackbone as the polymer chain: e.g., —C—C—C—C—C—C—C—C—C—C—Cx-, wherein xis the number of additional carbon atoms present to provide togetherwith the substituents on the polymer chain the molecular weight desiredfor the fluoropolymer, and making the fluoropolymer solid.Fluoropolymers having molecular weights of at least 50,000 (Mn) arecommercially available, making it convenient to use these fluoropolymersin their thermally destabilizable form in the mixture of the presentinvention. Preferred fluoropolymers are those that are melt-processibletetrafluoroethylene copolymers, for example comprising at least 40-99mol % tetrafluoroethylene (TFE) derived (by polymerization) repeat unitsand 1-60 mol % of units derived from at least one other comonomer.Preferred comonomers with TFE to form perfluoropolymers areperfluoroolefins having 3 to 8 carbon atoms, such as hexafluoropropylene(HFP), and/or perfluoro(alkyl vinyl ether) (PAVE) in which the linear orbranched alkyl group contains 1 to 5 carbon atoms. Preferred PAVEmonomers in these TFE copolymers and those described below are those inwhich the alkyl group contains 1, 2, or 3 carbon atoms, and thecopolymer can be made using several PAVE monomers. Preferred TFEcopolymers include FEP (TFE/HFP copolymer and TFE/HFP/PAVE copolymer)and PFA (TFE/PAVE copolymer), wherein PAVE is most preferablyperfluoro(ethyl vinyl ether) (PEVE) or perfluoro(propyl vinyl ether)(PPVE), or the combination of perfluoro(methyl vinyl ether) (PMVE) andPPVE, i.e. TFE/PMVE/PPVE copolymer, sometimes referred to as MFA in thisfield. Less preferred is a fluoropolymer that has —CH₂— units in thepolymer chain, such as THV (TFE/HFP/VF₂ copolymer). The FEP preferablycontains 5 to 17 wt % HFP, the remainder being TFE, with PAVE content ifpresent being 0.2 to 2 wt % based on the total weight of the FEP. ThePFA preferably contains at least 2 wt % PAVE, the remainder being TFE,based on the total weight of the PFA.

The fluoropolymer is at least 50 wt % fluorine, preferably at least 60wt %, and more preferably at least 70 wt % fluorine, based on the totalweight of the polymer chain (excludes end groups). In one embodiment ofthe present invention, if hydrogen is present in the repeat units makingup the polymer chain, it is preferred that hydrogen is onlymono-substituted on any of the carbon atoms making up the polymer chainor in any side group bonded to the polymer chain, since the presence of—CH₂— can impair the non-flammability of the fluoropolymer. Preferably,the hydrogen content, if any, is no greater than 2 wt %, more preferablyno greater than 1 wt %, most preferably no greater than 0.5 wt %, basedon the total weight of the fluoropolymer. A small amount of hydrogenalong the polymer chain can have the beneficial effect of thermallydestabilizing the fluoropolymer, thereby assisting its combustionabatement effect. The small amount of hydrogen present in thefluoropolymer contributes to the abatement of combustion by the mode ofaction (v). In another embodiment of the present invention, thefluoropolymer is a perfluoropolymer. By perfluoropolymer is meant thatthe monovalent substituents on the carbon atoms forming the polymerchain of the polymer are all fluorine atoms, with the possible exceptionof end groups.

In contrast to the fluoropolyether combustion abatement agent, which isin the liquid state, the fluoropolymer is in the solid state at least atthe normal operating conditions encountered by the Li-ion battery, up to40° C., sometimes up to 50° C. and higher, e.g. up to 60° C. and even upto 80° C. at the pressure of one atmosphere. At higher temperatures, thefluoropolymer may melt. Preferably, however, the melting temperature ofthe fluoropolymer is at least 200° C. and not greater than 315° C.Alternatively, the fluoropolymer may be one which softens upon heating,rather than having a distinct melting temperature. In either case, thefluoropolymer is preferably melt flowable. Nevertheless, thefluoropolymer remains solid at the normal operating conditions of theLi-ion battery. The melt flowability can be characterized by a melt flowrate (MFR) of at least 0.01 g/10 min, preferably at least 0.1 g/10 min,more preferably at least 5 g/10 min or at least 10 g/10 min, all asmeasured in accordance with ASTM D 1238, under conditions of melttemperature and weight on the molten polymer that is prescribed for theparticular fluoropolymer. For PFA and FEP, the prescribed temperatureand weight is 372° C. and 5 kg, respectively.

The fluoropolymers are known for their thermal stability, especiallyarising from the strong chemical bonding between carbon and fluorineatoms predominating in the fluoropolymer. It is common, however, for theas-polymerized solid fluoropolymer to have thermally unstable moieties,especially unstable end groups, arising from ingredients providing freeradicals in the aqueous polymerization medium during the polymerizationreaction. As many or more than a total of at least 300 unstable endgroups, more often at least 400 such end groups —COOH, —COF, and/or—CONH₂. Per 10⁶ carbon atoms can be present in the as-polymerizedfluoropolymer. For example, the common persulfate polymerizationinitiator in the aqueous polymerization medium results in the formationof carboxyl end groups, —COOH, on the polymer chain. These groupsdecompose at elevated temperatures, indicating the thermal instabilityof the fluoropolymer. The decomposition is the splitting off of thecarboxyl end groups, leaving behind the reactive group CF₂ ⁻, which canlead to the formation of a new unstable end group, perfluorovinyl,—CF═CF₂, extending into the polymer chain. Before such destabilizablefluoropolymers are made available by the manufacturer for commercialuse, the fluoropolymer is subjected to a stabilization process thatreplaces unstable end groups by stable end groups. For example, FEP issubjected to humid heat treatment at high temperatures to replaceunstable end groups by the stable —CF₂H end group. Both FEP and PFA aresubjected to fluorination treatment to replace unstable end groups bythe stable —CF₃ end group.

The destabilizable fluoropolymer used as a combustion abatement agent inthe present invention is preferably not end-group stabilized, but isinstead used in its thermally destabilizable form, i.e. the thermallyunstable moieties such as the unstable end groups are present in thefluoropolymer. The heating up by the Li-ion battery caused by suchcorruption as improper recharging or short circuiting results in theheating of the fluoropolymer to cause decomposition of unstablemoieties. This decomposition results in non-combustible volatiles beingemitted from the fluoropolymer. These volatiles abate combustion, eitherpreventing it from occurring, confining it if it does occur, orinstantaneously extinguishing the fire. The combustion volatiles provideat least mode of action (v) in combustion abatement.

A preferred destabilizable fluoropolymer is the FEP mentioned above, butwith end groups not being stabilized, so as to possess the unstable endgroups mentioned above.

Another embodiment of thermally destabilizable fluoropolymer is thefluoropolymer that contains thermally destabilizable groups, such as—CH₂—CH₂— or —CH₂—, in the polymer chain in the small amount asmentioned above that provides thermal decomposition of the fluoropolymerwithout imparting flammability to the fluoropolymer. Such thermallyunstable groups can be present in combination with thermally unstableend groups such as disclosed above. A preferred thermally destabilizablefluoropolymer that contains at least polymer (main) chain thermallyinstability is the copolymer of TFE, HFP and ethylene, with the amountof ethylene in the copolymer being small to satisfy the preferredmaximum hydrogen contents mentioned above. The TFE and HFP contents ofthe TFE/HFP/ethylene copolymer can be the same as for the FEP dipolymermentioned above.

The thermally destabilizable fluoropolymer is preferably one thatbecomes flowable under the heating provided by the corrupted Li-ionbattery. In the case of fluoropolymers that have a melting temperature,such heating exceeds the melting temperature. The fluoropolymer eithersoftens sufficiently upon such heating that it becomes molten andflowable or melts to become melt flowable. The heating provided by thecorrupted battery changes the fluoropolymer from the solid state to theliquid state. This flowing of the fluoropolymer contributes to theexclusion of oxygen from combustible vapors arising from overheatedelectrolyte, and/or containment of the fire. The melt flow can besufficient to seal the Li-ion battery from which combustible vaporswould otherwise escape.

The thermally destabilizable fluoropolymer can be fabricated into sheetsthat can be used as insulators such as top and bottom insulators 22 and24 (FIGS. 1, 3, and 6) and top insulator 74 such as by compressionmolding at a temperature just above the melting temperature of thefluoropolymer.

In another embodiment of the present invention, the combustion abatementagent used in the present invention is a combination of combustionabatement agents. This combination can expose the corrupted Li-ionbattery, the region of electrochemical activity 20 where the corruptionis occurring, to multiple modes of action for abating combustion. Thiscombination can make use of the liquid fluoropolyether combustionabatement agent, but in a semi-solid form that may be more convenientfor application within the Li-ion battery. This conversion from theliquid state to semi-solid state is done by mixing with the liquidfluoropolyether particulate combustion abatement agent such as thosedescribed above, whether an inorganic compound, an organic compound, orsolid fluoropolymer in an amount effective to obtain the semi-solidstate.

By semi-solid (state) is meant, that the composition is not a liquidunder the normal conditions of temperature and pressure mentioned above.Preferably, this semi-solid state persists at the higher temperaturesencountered in the normal operation of that the Li-ion battery,including recharging, when the battery is a rechargeable battery. Normaloperation of the battery can include ambient temperature (15-25° C.) andhigher temperatures up to 40° C., sometimes up to 50° C. and evenhigher, e.g. temperatures up to 60° C. and even up to 80° C. and forsimplicity, under a pressure of one atm. The semi-solid state of thecomposition differs from the liquid state by not being flowable at anyof these temperatures and pressure conditions. In contrast, the liquidstate denotes flowability so as to take the shape of its container,while having a fixed volume. Instead of flowability, the semi-solidstate of the composition means that it has rigidity, whereby it stayswhere it is positioned with respect to the battery. This positioning ofthe composition is facilitated by the characteristic of the semi-solidstate of the mixture, namely that the mixture is flowable enough underpressure for achieving intimate contact with desired surfaces withrespect to the battery, e.g. the filling of a chamber such as chambers28, 42, and 54. The applied pressure may be only that of a hand trowelused to apply, spread, or pack the semi-solid to achieve the contact orfilling desired. Once applied and the pressure is removed, thesemi-solid state of the fluorinated material results it not flowing awayfrom its applied position under the normal conditions of the Li-ionbattery. Characteristic of being semi-solid, the composition in thissemi-solid state has the consistency of wax, dough, or putty, thestiffness of which can be controlled for example by the molecular weightof the fluoropolyether, the amount solid additive to the resultantcomposition to thicken it to become the semi-solid state, and theparticle size of the solid additive when the fluoropolyether and solidadditive, which can be combustion abatement agent as mentioned above,are mixed together. In any event, the molecular weight of thefluoropolyether is low enough that it is in the liquid state undernormal conditions and preferably under the normal operating conditionsof the Li-ion battery, whereby the liquid fluoropolyether would have aboiling temperature (at one atm) greater than 80° C. The semi-solidstate can be characterized by exhibition of a tensile strength of zerotypically by virtue of the inability to form tensile test specimens thathave sufficient integrity to be tensile strength tested.

Another solid fluoropolymer that can be added to liquid fluoropolyetherfor thickening it to form a mixture that has the semi-solid state is lowmolecular weight polytetrafluoroethylene, which is commonly known asPTFE micropowder, so as to distinguish from polytetrafluoroethylene(PTFE), which has such a high molecular weight that it does not flow inthe molten state described above. While the molecular weight of PTFEmicropowder is low relative to PTFE, it is high enough to provide asolid polymer. As solid polymer, the PTFE micropowder is commerciallyavailable as a powder, which maintains is powder state by not beingputty-like, i.e. the PTFE micropowder is not in a semi-solid state.Instead, the PTFE micropowder in the powder state form consists ofparticles sufficiently hard that the PTFE micropowder in powder form isfree flowing. The result of the lower molecular weight of PTFEmicropowder than PTFE is that it has fluidity in the molten state, i.e.melt flowability. The melt flowability of PTFE micropowder can becharacterized by a melt flow rate (MFR) of at least 0.01 g/10 min,preferably at least 0.1 g/10 min and more preferably at least 5 g/10min, and still more preferably at least 10 g/10 min, as measured inaccordance with ASTM D 1238, at 372° C. using a 5 kg weight on themolten polymer. The PTFE micropowder by itself is not melt fabricable,i.e. an article molded from the melt of PTFE micropowder is useless, byvirtue of extreme brittleness. Because of its low molecular weight(relative to non-melt-flowable PTFE), it has no strength. An extrudedfilament of PTFE micropowder is so brittle that it breaks upon flexing.

The combustion abatement agent that is a combination of materials can bemade by mixing the materials together, preferably wherein one of thesematerials is the liquid fluoropolyether and preferably at least oneother component of the mixture is a different combustion abatementagent, preferably to obtain the resultant composition being in thesemi-solid state as described above. If solid fluoropolymer and/ordecomposition catalyst are to be present in the composition, these canbe included in the mixing step. The particles of the solid fluoropolymercan be those that result from the polymerization process to make thefluoropolymer. For example, aqueous dispersion polymerization typicallyresults in the formation of fluoropolymer particles having an averageparticle size of no greater than 0.5 micrometers as measured by laserlight scattering. Recovery of the fluoropolymer particles from theaqueous polymerization medium results in aggregation of the primaryparticles from the polymerization process to form secondary particles ofagglomerated primary particles, the secondary particles typically havingan average particle size of 200 to 800 micrometers as measured by laserlight scattering (ASTM D 4464). The particle size of the addedcombustion abatement agent as a compound, solid fluoropolymer, andcatalyst is preferably that which is effective to produce a homogeneoussemi-solid mixture with the liquid fluoropolyether. Preferably theaverage particle size (by light scattering according to ASTM D 4464) ofthese components is in the range of 0.1 to 800 micrometers).

The mixing step can be carried out at ambient temperature (15-25° C.)for convenience. The mixing can be carried out by hand or by mechanicalmeans. The components are added to the mixing vessel and subjected tomixing. When a particulate solid is being mixed preferably with aliquid, the mixture is complete when no concentration of eithercomponent is visible. Instead, a homogeneously appearing mixture, thatis preferably semi-solid, is obtained. It is preferred that homogeneityis retained during the use of the composition over the life of theLi-ion battery, but this homogeneity can be unnecessary when thecomposition is applied in confinement with respect to the Li-ionbattery. Confinement of the composition maintains the presence of thecomponents of the composition even when separated within the confinementspace (chamber).

With respect to proportions of components in the combustion abatementagent as a composition, the amount of particulate solid materials orsimply particulate solids, whether being combustion abatement agentother than fluoropolymer or the combination of such combustion abatementagent and fluoropolymer, whether thermally destabilizable or justfluoropolymer thickener, present in the composition is preferablyeffective to convert the liquid state of the fluoropolyether tosemi-solid state. This amount will depend on the molecule weight of thefluoropolyether and the particle size of the solids present and theamount of the solids being mixed. The higher the molecular weight of thefluoropolyether, the higher is its viscosity, meaning that less of theparticulate solids will be needed for the conversion to the semi-solidstate. The smaller the particle size of the particulate solids, the lessof these solids will be needed to accomplish this conversion. Withrespect to the particulate solids being combustion abatement agent otherthan fluoropolymer, it is preferred that the semi-solid compositioncomprises at least 70 wt %, more preferably at least 60 wt %, and mostpreferably at least 50 wt % liquid fluoropolyether, the remainder tototal 100 wt % being the particulate solids. It is also preferred thatat least 3, 4, or 5 wt % of the composition comprises the particulatesolids, the remainder to total 100 wt % being the liquidfluoropolyether, whereby the maximum amount of liquid fluoropolyether is97 wt %, 96 wt %, and 95 wt %, respectively. Additional preferredminimums of particulate solids applicable to the are at least 10 wt %,at least 15 wt %, at least 20 wt % at least 25 wt %, at least 30 wt %,at least 35 wt %, or at least 40 wt %, the remainder to total 100 wt %being the combination of liquid fluoropolyether and particulate solids.In one embodiment, these composition ranges apply to the combination ofliquid fluoropolyether and combustion abatement agent(s) other thanfluoropolymer as the particulate solid, to total 100 wt %. In anotherembodiment, these composition ranges apply to the combination of liquidfluoropolyether, and combustion abatement agent other than fluoropolymerand/or fluoropolymer as particulate solids, whether PTFE micropowder orthermally destabilizable fluoropolymer, this combination together withthe liquid fluoropolyether totaling 100 wt % of the composition of thesecomponents. According to this embodiment, the weight % of particulatesolids mentioned above apply to the combination of combustion abatementagent other than fluoropolymer and fluoropolymer. Preferably, however,at least 3, 4, or 5 wt %, at least 10 wt %, at least 20 wt %, at least25 wt %, or at least 30 wt % of the combined weight of the liquidfluoropolyether, combustion abatement agent other than fluoropolymer,and fluoropolymer, is the combustion abatement agent other thanfluoropolymer. Preferably, the fluoropolymer component comprises atleast 50 wt % of the thermally destabilizable fluoropolymer. Thedecomposition catalyst amount, if any is present, in the composition isnot included in these composition ranges. The catalyst amount is basedon the weight of fluoropolyether as mentioned above.

EXAMPLES Example 1

The cathode electrode for the lithium cylindrical cell was fabricatedfrom a mixture of LiMn0.33Ni0.33Co0.33O₂ electrode powder,polyvinylidene difluoride (PVDF) polymer binder, and graphite slurriedin 1-methyl-2-pyrrolidinone (NMP). The anode electrode was fabricatedfrom graphite, PVDF and NMP. The cathode electrode was cast from theslurry onto an aluminum current collector foil and on a copper currentcollector foil for anode electrode. The electrolyte was 1 M LiPF₆ inethylene carbonate (EC):diethyl carbonate (DEC). A polypropyleneseparator was used in the process to wind a battery cell core. The woundcore elements (jelly roll) were inserted in a metal can depicted in FIG.1, closed and sealed. The metal can assembly as depicted in FIG. 1 has asteel can 6 and a steel battery top 8, which is the positive pole of thebattery. The can 6 is the negative pole of the battery. The two polesare insulated from one another by a u-shaped polymer insulator ring 10positioned between the positive and negative poles where proximate toone another. Positioned within the u-shape of the insulator ring 10 area disc 12 having an aperture 14 therewithin and a scored polyamiderupture disc 16 forming a closure of aperture 14, all pressed togetherby the crimp 18 encircling the can 6 as shown. The wound core elements(region of electrochemical activity 20) within the battery sits insideinsulated sides of the can 6 and sheet insulators 22 and 24 covering thetop and bottom, respectively, of the wound core elements. A center pin26 sits in the center of the wound core elements. The insulators 22 and24 are both sheets of flame retardant polyvinyl alcohol. The spacebetween the top insulator 22 and rupture disc 16 forms chamber 28containing combustion abatement agent.

The assembled battery cell was fully charged and then a nail was driventhrough the sides of the can so that the nail penetrates partway throughthe wound core elements shorting the charged battery resulting in arapid temperature increase inside the battery. Pressure builds insidethe battery can assembly until the top insulator 22 failed exposing thecombustion abatement material, in this case an 80:20 (by weight) mixtureof PFPE and Al(OH)₃, in chamber 28 to wound core elements that arerapidly increasing in temperature above 100° C. Rapidly there is ageneration of smoke and a flame that was presumably sparked by arcingfrom the shorting process in the battery. The combustion abatementmaterial quickly extinguished the flame and the wound core elementsbegan to cool. Within a few minutes the entire battery cell assemblytemperature dropped below 100° C. and posed no fire hazard.

The PFPE used in the experiment of this Example and in the experimentsof the remaining Examples is the PFPE (fluorinated composition) used inExample 1 of U.S. Patent Publication 2014/0065461.

Example 2

The wound core elements (jelly roll) were identical to EXAMPLE 1. Thewound core elements (jelly roll) were inserted in a metal can depictedin FIG. 1, closed and sealed. The metal can assembly as depicted in FIG.1 has a steel can 6 and a steel battery top 8, which is the positivepole of the battery. The can 6 is the negative pole of the battery. Thetwo poles are insulated from one another by a u-shaped polymer insulatorring 10 positioned between the positive and negative poles whereproximate to one another. Positioned within the u-shape of the insulatorring 10 are a disc 12 having an aperture 14 therewithin and a scoredpolyamide rupture disc 16 forming a closure of aperture 14, all pressedtogether by the crimp 18 encircling the can 6 as shown. The wound coreelements (region of electrochemical activity 20) within the battery sitsinside insulated sides of the can 6 and sheet insulators 22 and 24covering the top and bottom, respectively, of the wound core elements. Acenter pin 26 sits in the center of the wound core elements. Theinsulators 22 and 24 are both sheets of flame retardant polyvinylalcohol. An additional chamber 42 is included and filled with the samecombustion abatement agent as chamber 28.

The assembled battery cell was fully charged and then a nail was driventhrough the sides of the can so that the nail penetrates partway throughthe wound core elements shorting the charged battery resulting in arapid temperature increase inside the battery. Pressure builds insidethe battery can assembly until the top and bottom insulators 22 and 24failed exposing the combustion abatement material, in this case an 80:20(by weight) mixture of PFPE and Al(OH)₃, in chambers 28 and 42 to woundcore elements that are rapidly increasing in temperature above 100° C.Rapidly there is a generation of smoke and a flame that was presumablysparked by arcing from the shorting process in the battery. Thecombustion abatement material quickly extinguished the flame and thewound core elements began to cool. Within a few minutes the entirebattery cell assembly temperature dropped below 100° C. and posed nofire hazard.

Example 3

The wound core elements (jelly roll) were identical to EXAMPLE 1. Thewound core elements (jelly roll) were inserted in a metal can depictedin FIG. 3 with the exception that chamber 28 was empty and did notcontain any combustion abatement agent, closed and sealed. Thecombustion abatement agent is located only in chamber 42. The metal canassembly as depicted in FIG. 3 has a steel can 6 and a steel battery top8, which is the positive pole of the battery. The can 6 is the negativepole of the battery. The two poles are insulated from one another by au-shaped polymer insulator ring 10 positioned between the positive andnegative poles where proximate to one another. Positioned within theu-shape of the insulator ring 10 are a disc 12 having an aperture 14therewithin and a scored polyamide rupture disc 16 forming a closure ofaperture 14, all pressed together by the crimp 18 encircling the can 6as shown. The wound core elements (region of electrochemical activity20) within the battery sits inside insulated sides of the can 6 andsheet insulators 22 and 24 covering the top and bottom, respectively, ofthe wound core elements. A center pin 26 sits in the center of the woundcore elements. The insulators 22 and 24 are both sheets of flameretardant polyvinyl alcohol.

The assembled battery cell was fully charged and then a nail was driventhrough the sides of the can so that the nail penetrates partway throughthe wound core elements shorting the charged battery resulting in arapid temperature increase inside the battery. Pressure builds insidethe battery can assembly until the top and bottom insulators 22 and 24failed exposing the combustion abatement material, in this case an 80:20(by weight) mixture of PFPE and Al(OH)₃, in chamber 42 to wound coreelements that are rapidly increasing in temperature above 100° C. Apartial vacuum forms in chamber 28 after the rupture disc 16 fails andgases begin to escape through the top of the battery can assistingdrawing the combustion agent in chamber 42 to come into contact with thewound core elements in the region of electrochemical activity 20.Rapidly there is a generation of smoke and a flame that was presumablysparked by arcing from the shorting process in the battery. Thecombustion abatement material quickly extinguished the flame and thewound core elements began to cool. Within a few minutes the entirebattery cell assembly temperature dropped below 100° C. and posed nofire hazard.

Example 4

The wound core elements (jelly roll) were identical to EXAMPLE 1. Thewound core elements (jelly roll) were inserted in a metal can depictedin FIG. 1 with the exception that chamber 28 was empty and did notcontain any combustion abatement agent, closed and sealed. A multilayersheet 48 containing combustion abatement agent as depicted in FIG. 4 andFIG. 5, was placed around wound core elements before insertion into thecan, then the can is closed and sealed. The sheet 48 was made of films50 and 52, which were flame retardant polyvinyl alcohol, and the chamber54 was filled with combustion abatement agent. The entire battery cellhas a steel can 6 and a steel battery top 8, which is the positive poleof the battery. The can 6 is the negative pole of the battery. The twopoles are insulated from one another by a u-shaped polymer insulatorring 10 positioned between the positive and negative poles whereproximate to one another. Positioned within the u-shape of the insulatorring 10 are a disc 12 having an aperture 14 therewithin and a scoredpolyamide rupture disc 16 forming a closure of aperture 14, all pressedtogether by the crimp 18 encircling the can 6 as shown. The wound coreelements (region of electrochemical activity 20) within the battery sitsinside insulated sides of the can 6 and sheet insulators 22 and 24covering the top and bottom, respectively, of the wound core elements. Acenter pin 26 sits in the center of the wound core elements. Theinsulators 22 and 24 are both sheets of flame retardant polyvinylalcohol.

The assembled battery cell was fully charged and then a nail was driventhrough the sides of the can so that the nail penetrates partway throughthe wound core elements shorting the charged battery resulting in arapid temperature increase inside the battery. Temperature and pressurerises inside the battery can assembly until the top and bottominsulators 22 and 24 and the films of flame retardant polyvinyl alcohol50 and 52 failed exposing the combustion abatement agent 50, in thiscase an 80:20 (by weight) mixture of PFPE and Al(OH)₃, to wound coreelements that are rapidly increasing in temperature above 100° C. Apartial vacuum forms in chamber 28 after the rupture disc 16 fails andgases begin to escape through the top of the battery can assistingdrawing the combustion agent to come into contact with the wound coreelements in the region of electrochemical activity 20. Rapidly there isa generation of smoke and a flame that was presumably sparked by arcingfrom the shorting process in the battery. The combustion abatementmaterial quickly extinguished the flame and the wound core elementsbegan to cool. Within a few minutes the entire battery cell assemblytemperature dropped below 100° C. and posed no fire hazard.

Example 5

The wound core elements (jelly roll) were identical to EXAMPLE 1. Thewound core elements (jelly roll) were inserted in a metal can depictedin FIG. 1, closed and sealed. The metal can assembly as depicted in FIG.1 has a steel can 6 and a steel battery top 8, which is the positivepole of the battery. The can 6 is the negative pole of the battery. Thetwo poles are insulated from one another by a u-shaped polymer insulatorring 10 positioned between the positive and negative poles whereproximate to one another. Positioned within the u-shape of the insulatorring 10 are a disc 12 having an aperture 14 therewithin and a scoredpolyamide rupture disc 16 forming a closure of aperture 14, all pressedtogether by the crimp 18 encircling the can 6 as shown. The wound coreelements (region of electrochemical activity 20) within the battery sitsinside insulated sides of the can 6 and sheet insulators 22 and 24covering the top and bottom, respectively, of the wound core elements. Acenter pin 26 sits in the center of the wound core elements. Theinsulators 22 and 24 are both sheets of flame retardant polyvinylalcohol. The space between top insulator 22 and rupture disc 16 formschamber 28 containing combustion abatement agent.

The assembled battery cell was fully charged and then a nail was driventhrough the sides of the can so that the nail penetrates partway throughthe wound core elements shorting the charged battery resulting in arapid temperature increase inside the battery. Pressure builds insidethe battery can assembly until the top insulator 22 failed exposing thecombustion abatement material, in this case an 80:20 (by weight) mixtureof PFPE and Al(OH)₃ as well as a small amount of the Lewis Acid BF₃evenly dispersed in this mixture, in chamber 28 to wound core elementsthat are rapidly increasing in temperature above 100° C. Rapidly thereis a generation of smoke and a flame that was presumably sparked byarcing from the shorting process in the battery. The combustionabatement material quickly extinguished the flame and the wound coreelements began to cool. Within a few minutes the entire battery cellassembly temperature dropped below 100° C. and posed no fire hazard.

Example 6

The wound core elements (jelly roll) were identical to EXAMPLE 1. Thewound core elements (jelly roll) were inserted in a metal can depictedin FIG. 1, closed and sealed. The metal can assembly as depicted in FIG.1 has a steel can 6 and a steel battery top 8, which is the positivepole of the battery. The can 6 is the negative pole of the battery. Thetwo poles are insulated from one another by a u-shaped polymer insulatorring 10 positioned between the positive and negative poles whereproximate to one another. Positioned within the u-shape of the insulatorring 10 are a disc 12 having an aperture 14 therewithin and a scoredpolyamide rupture disc 16 forming a closure of aperture 14, all pressedtogether by the crimp 18 encircling the can 6 as shown. The wound coreelements (region of electrochemical activity 20) within the battery sitsinside insulated sides of the can 6 and sheet insulators 22 and 24covering the top and bottom, respectively, of the wound core elements. Acenter pin 26 sits in the center of the wound core elements. Theinsulators 22 and 24 are both sheets of flame retardant polyvinylalcohol. The space between top insulator 22 and rupture disc 16 formschamber 28 containing combustion abatement agent.

The assembled battery cell was fully charged and then a nail was driventhrough the sides of the can so that the nail penetrates partway throughthe wound core elements shorting the charged battery resulting in arapid temperature increase inside the battery. Pressure builds insidethe battery can assembly until the top insulator 22 failed exposing thecombustion abatement material, in this case an 60:40 (by weight) mixtureof PFPE and thermally destabilizable fluoropolymer, namely FEP havingits end groups not stabilized thereby being thermally unstable, inchamber 28 to wound core elements that are rapidly increasing intemperature above 100° C. Rapidly there is a generation of smoke and aflame that was presumably sparked by arcing from the shorting process inthe battery. The combustion abatement material quickly extinguished theflame and the wound core elements began to cool. Within a few minutesthe entire battery cell assembly temperature dropped below 100° C. andposed no fire hazard.

Example 7

The wound core elements (jelly roll) were identical in compositions andelectrode/separator construction to EXAMPLE 1, except the jelly roll wasflattened into a typical shape of a prismatic battery. The flattenedwound core elements region of electrochemical activity 20) were insertedinto a pouch constructed from a multilayer sheet 48 such as depicted inFIG. 4 and FIG. 5, closed and sealed. The film 52 of the sheet 48 is analuminum foil having an outer layer of polyamide and layer ofpolypropylene on the inside, with the chamber 54 containing combustionabatement agent. Film 50 is of flame retardant polyvinyl alcohol facingand in contact with the wound core elements forming the region ofelectrochemical activity. Separate metal tabs were connected to thewound core elements and individually extend outside the pouch for thepositive and negative poles of the “prismatic” battery.

The assembled battery cell was fully charged and then a nail was driventhrough the sides of the pouch so that the nail penetrates partwaythrough the wound core elements shorting the charged battery resultingin a rapid temperature increase inside the battery. As temperature andpressure rises inside the battery pouch assembly the flame retardantpolyvinyl alcohol film 52 is breeched exposing the combustion abatementagent, in this case an 80:20 (by weight) mixture of PFPE and Al(OH)₃.Rapidly there is a generation of smoke and a flame that was presumablysparked by arcing from the shorting process in the battery. Thecombustion abatement agent quickly extinguished the flame and the woundcore elements began to cool. Within a few minutes the entire batterycell assembly temperature dropped below 100° C. and posed no firehazard.

Essentially the same result was obtained in the experiments in theforegoing EXAMPLES when the combustion abatement agent used therein wasseparately replaced by the following compositions: (a) 95 w % of thePFPE and 5 wt % of hydrated magnesium silicate and (b) 67 wt % of thePFPE and 33 wt % of the thermally destabilizable fluoropolymer used inEXAMPLE 6.

What is claimed is:
 1. A Li-ion battery comprising an enclosure, whereinsaid enclosure is a can, structure defining a region of Li-ionelectrochemical activity positioned within said enclosure, saidstructure including oppositely charged electrodes for attracting Li-ionsfrom one said electrode to another said electrode, structure defining atleast one chamber positioned within said enclosure separate from saidregion of Li-ion electrochemical activity, said region of Li-ionelectrochemical activity being subject to overheating byshort-circuiting occurring within said region of Li-ion electrochemicalactivity, said chamber containing combustion abatement agent maintainedseparate from said region of Li-ion electrochemical activity, whereinsaid enclosure includes a vent for pressure release upon saidoverheating occurring within said region of Li-ion batteryelectrochemical activity, and said chamber containing said combustionabatement agent is positioned between said vent and said region ofLi-ion electrochemical activity, said structure defining said chambercontaining said combustion abatement agent including a membrane that isbreachable by said overheating to thereby release said combustionabatement agent into said region of electrochemical activity to abatecombustion therewithin, with the proviso that when said membranecomprises combustion abatement agent, the presence of said combustionabatement agent in said chamber is optional.
 2. The Li-ion battery ofclaim 1 wherein said membrane is breachable by said overheating causingrupture of said membrane.
 3. The Li-ion battery of claim 1 wherein saidmembrane is breachable by said overheating causing melting of saidmembrane.
 4. The Li-ion battery of claim 1 wherein said membrane isinert to the Li-ion electrochemical activity occurring within saidregion of Li-ion electrochemical activity.
 5. The Li-ion battery ofclaim 1 wherein said vent includes a closure that opens to permit saidpressure release, the opening of said vent accompanying the rupture ofsaid membrane.
 6. The Li-ion battery of claim 1 wherein said vent ispositioned at one end of said enclosure and an additional chamberincluding a membrane that is breachable by said overheating andcontaining combustion abatement agent is positioned remote from saidchamber positioned between said vent and said region of Li-ionelectrochemical activity, whereby said combustion abatement agent fromeach said chambers is released into said region of Li-ionelectrochemical activity upon said overheating to thereby abatecombustion within said region of Li-ion electrochemical activity.
 7. TheLi-ion battery of claim 1 wherein said combustion abatement agent is acomposition comprising liquid fluoropolyether.
 8. The Li-ion battery ofclaim 7 wherein said composition additionally comprises decompositioncatalyst and/or solid material.
 9. The Li-ion battery of claim 8 whereinsaid solid material is additional combustion abatement agent.
 10. TheLi-ion battery of claim 8 wherein said composition resulting from saidliquid fluoropolyether and said solid material is a semi-solid.
 11. TheLi-ion battery of claim 7 wherein said combustion abatement agent is notin contact with said region of electrochemical activity.
 12. The Li-ionbattery of claim 7 wherein said liquid fluoropolyether is aperfluoropolyether.
 13. The Li-ion battery of claim 7 wherein saidcomposition additionally comprises decomposition catalyst comprising aLewis acid.
 14. The Li-ion battery of claim 1 wherein said membranecomprises a thermally destabilizable fluoropolymer.
 15. The Li-ionbattery of claim 14 wherein said thermally destabilizable fluoropolymeris selected from the group consisting of atetrafluoroethylene/hexafluoropropylene copolymer and atetrafluoroethylene/hexafluoropropylene/perfluoro(alkyl vinyl ether)copolymer.
 16. Li-ion battery of claim 15 wherein said thermallydestabilizable fluoropolymer has at least 300 unstable end groups per10⁶ carbon atoms, said endgroups being selected from the groupconsisting of —COOH, COF, and —CONH₂.